1. Field of the Invention
The present invention relates to an optical system suited for the reproduction of especially a color manuscript, more particularly, an optical system presenting substantially symmetrical lenses comprising some lenses which are somewhat unsymmetrical, whereby the lenses for projecting the manuscript are of symmetrical arrangement, while a space in which the filter is to be inserted, is provided.
2. Disclosure of the Prior Art
For the image forming lens with almost an equal magnification factor to be used for the manuscript reproduction machine capable of reproducing the color manuscript, it has to be taken into consideration that the lens should have a good permeability for the light beam with wave length 400 m.mu. to 700 m.mu. (from the blue light to the red light), that the chromatic aberration should strictly be compensated and that the filter as means for color resolution can be inserted in the optical path.
Hereby, the place in which the filter should be provided is thought to be between the light source for illuminating the manuscript to be reproduced and the manuscript. However, in the case of the ordinary reproduction machine, a light source in the form of a bar with a length nearly corresponding to the width of the manuscript is provided close to the above mentioned manuscript in order to obtain a homogeneous illumination.
Therefore, if a filter should be provided between the light source and the surface of the manuscript, the size of the filter would be large, because the length of the filter should be nearly equal to the width of the manuscript, whereby further the filter would be apt to be damaged due to the influence of the heat produced by the light source, which is very inconvenient. Further it is conceivable that the filter could be provided between the reproducing optical system and the light sensitive body, whereby the size of the filter would also be large.
Further, in the case of color reproduction, three kinds of filters in accordance with the three primary colors are provided so as to be put in and taken out of the reproduction optical system for the production of one manuscript in such a manner that the reproduction is carried out for each filter and the colors are composed on the photosensitive body so as to reproduce the color manuscript. Thus at least three filters in accordance with the primary color of the light are necessary whereby it is necessary to form the filters as small as possible in order to prevent the mechanism for the exchange of the filters from becoming large so as to facilitate the exchange of the filters.
Thus the objects of the present invention are as follows, the above being taken into consideration.
The first object of the present invention is to offer an optical system, designed to be compact, as a color reproduction optical system with a plural number of filters.
The second object of the present invention is to offer an image forming lens with good permeability in the range of visible light (400 m.mu.-700 m.mu.).
The third object of the present invention is to offer an image forming lens whose aberrations, especially chromatic aberrations are strictly compensated.
Further other objects and features of the present invention will be disclosed hereinbelow.